1. Field of the Invention
This invention relates to a process for the production of mixtures of glyoxylic acid and a dialkyl aminomethylphosphonate, where glycolic acid and oxygen are reacted in an aqueous solution, in the presence of a dialkyl aminomethylphosphonate and catalysts consisting of glycolate oxidase ((S)-2-hydroxyacid oxidase, EC 1.1.3.15) and catalase (EC 1.11.1.6). The resulting mixtures of glyoxylic acid and dialkyl aminomethylphosphonate produced in this manner are useful intermediates in the production of N-(phosphonomethyl)glycine, a broad-spectrum, post-emergent phytotoxicant and herbicide useful in controlling the growth of a wide variety of plants.
2. Description of the Related Art
Glycolate oxidase, an enzyme commonly found in leafy green plants and mammalian cells, catalyzes the oxidation of glycolic acid to glyoxylic acid, with the concomitant production of hydrogen peroxide: EQU HOCH.sub.2 CO.sub.2 H+O.sub.2 .fwdarw.OCHCO.sub.2 H+H.sub.2 O.sub.2
N. E. Tolbert et al., J. Biol. Chem., Vol. 181,905-914 (1949) first reported an enzyme, extracted from tobacco leaves, which catalyzed the oxidation of glycolic acid to formic acid and CO.sub.2 via the intermediate formation of glyoxylic acid. The addition of certain compounds, such as ethylenediamine, limited the further oxidation of the intermediate glyoxylic acid. The oxidations were carried out at a pH of about 8, typically using glycolic acid concentrations of about 3-40 mM (millimolar). The optimum pH for the glycolme oxidation was reported to be 8.9. Oxalic acid (100 mM) was reported to inhibit the catalytic action of the glycolate oxidase. Similarly, K. E. Richardson and N. E. Tolbert, J. Biol. Chem., Vol. 236, 1280-1284 (1961) showed that buffers containing tris(hydroxymethyl)aminomethane (TRIS) inhibited the formation of oxalic acid in the glycolate oxidase catalyzed oxidation of glycolic acid. C. O. Clagett, N. E. Tolbert and R. H. Burris J. Biol. Chem., Vol. 178,977-987 (1949) reported that the optimum pH for the glycolate oxidase catalyzed oxidation of glycolic acid with oxygen was about 7.8-8.6, and the optimum temperature was 35.degree.-40.degree. C.
I. Zelitch and S. Ochoa, J. Biol. Chem., Vol. 201,707-718 (1953), and J. C. Robinson et al., J. Biol. Chem., Vol. 237, 2001-2009 (1962), reported that the formation of formic acid and CO.sub.2 in the spinach glycolate oxidase-catalyzed oxidation of glycolic acid resulted from the non-enzymatic reaction of H.sub.2 O.sub.2 with glyoxylic acid. They observed that addition of catalase, an enzyme that catalyzes the decomposition of H.sub.2 O.sub.2, greatly improved the yields of glyoxylic acid by suppressing the formation of fonnic acid and CO.sub.2. The addition of FMN (flavin mononucleotide) was also found to greatly increase the stability of the glycolate oxidase.
N. A. Frigerio and H. A. Hasbury, J. Biol. Chem., Vol. 231,135-157 (1958) have reported on the preparation and properties of glycolic acid oxidase isolated from spinach. The purified enzyme was found to be very unstable in solution; this instability was ascribed to the relatively weak binding of flavin mononucleotide (FMN) to the enzyme active site, and to the dissociation of enzymatically active tetramers and/or octamers of the enzyme to enzymatically-inactive monomers and dimers, which irreversibly aggregate and precipitate. The addition of FMN (flavin mononucleotide) to solutions of the enzyme greatly increased its stability, and high protein concentrations or high ionic strength maintained the enzyme as octamers or tetramers.
A process for the preparation of mixtures of glyoxylic acid and aminomethylphosphonic acid (AMPA) has been described in U.S. Pat. No. 5,135,860. Glycolic acid and oxygen were reacted in an aqueous solution and in the presence of AMPA and two enzyme catalysts, glycolate oxidase and catalase. This process demonstrated the synergistic effect of using both catalase (to destroy byproduct hydrogen peroxide responsible for formate production) and AMPA as an amine additive capable of forming oxidation-resistant N-substituted hemiaminal and/or imine complexes with glyoxylate (limiting its further oxidation). Yields of glyoxylic acid as high as 92% were reported, and the resulting mixtures of glyoxylic acid and AMPA were used for the preparation of N-(phosphonomethyl)glycine, a post-emergent phytotoxicant and herbicide.